1. Field of the Invention
The present invention relates to a filtering material for effectively and reliably adsorbing not only conventional foreign material such as dust, unpleasantly odoring gaseous substance or the like but also very fine infectious or antigenous foreign material such as virus, bacteria, fungus, pollen or the like. Further, the present invention relates to a method of producing a filtering material of the foregoing kind.
2. Description of the Related Art
As is well known for any expert in the art, a conventional filtering material employable for a mask or the like is generally constructed such that only fibers are directionally or undirectionally arranged to form a mesh-shaped laminated structure having a predetermined thickness. To improve gas adsorption properties of the filtering material, another conventional filtering material is constructed to form a different laminated structure, i.e., a sandwiched structure having a predetermined thickness such that a gas adsorbing agent such as an activated carbon or the like is interposed between two filtering materials each composed of fibers.
With respect to each of the conventional filtering materials as mentioned above, it has been confirmed from the results derived from a series of incubation tests that it can substantially reliably adsorb dust or unpleasantly odoring substance but it can hardly adsorb very fine infectious or antigenous foreign material such as virus, bacteria, fungus, pollen or the like.
For this reason, any one of the conventional filtering materials has a drawback that it can not suitably be employed for masks available for surgical operations, since virus, bacteria and fungus contained in a breath blown from a surgeon are undesirably scattered to a patient because of failure to adsorb them in the filtering material of a mask or virus, bacteria and fungus contained in a mist-shaped body fluid or blood scattered from the patient can not be removed by the mask born by the surgeon.
In addition, since each conventional filtering material can not substantially adsorb pollen scattered from cedars, other drawback of the conventional filtering material is that it can not practically be utilized as a filtering material for masks available for a pollinosis which has become a serious problem in this country in recent years.
When the conventional filtering materials are considered from the viewpoint of a production method, there arises a drawback that an inexpensive paper can not be used as a sheet-shaped raw material for the following reasons. One of them consists in that when a paper having poor toughness is immersed in a treatment solution bath, there is a possibility that the paper is broken or torn due to reduction of a strength of the paper itself after completion of the immersing operation. The other one consists in that when a paper having excellent toughness is used as a sheet-shaped raw material, it is difficult that porous apatite particles, one of components constituting the filtering material penetrates into fibers of the paper or the porous apatite particles adhesively deposited on the paper are liable to peel away from surfaces of the paper.
Alternatively, when a fibrous material is employed as a sheet-shaped raw material, there arises another drawback that porous apatite particles are locally gathered in a certain region until they are filled in the sheet-shaped raw material or sprayed on surfaces of the same and the sheet-shaped material filled or sprayed with the porous apatite particles is then thermally dried.